e, CBRIANTHARIA. 



As regards the directive mesenteries, it is no doubt true that their musculature is usually very 

 indistinct, still I believe that there will be no danger of going very far wrong if we assume the same 

 arrano-ement of musculature as original for these mesenteries also. Cerfontaine certainly states, 

 that the muscles on the directive mesenteries in A. oligopodus have the same orientation as on the 

 rest of the mesenteries. Further 1 have found the same arrangement in the well known Ceriantharian 

 larval form Arachnactis albida (fig. 8, pi. 5). The same seems also to be the case in C. valdiviac and 

 in the hemisulcus region of P. solitarius. 



It still remains to be explained, why van Benedeu in the case ol larval forms of Ceriantharia") 

 found a different arrangement of the mesenterial musculature from that above described. It may 

 possibly be, that with the growth of the larval forms the direction of the musculature shifts, and that 

 the transverse muscles are relativel\- late in appearing. Tlioirgli such an exjjlauation is not excluded, 

 still I think that we need not have recourse to such an hypothesis. It is more likely that van Bene- 

 den made a mistake, which is very easy, seeing that the mesenterial muscles are extremely faint in 

 the larval forms. Has not the arrangement of the mesenterial musculature in adult Ceriantharia, whose 

 musculature is many times better developed than in the larval forms, given rise to controversy, 

 and that for the reason that most observers have taken contracted specimens, where it was a difficult 

 matter to establish the direction of the muscles on mesenteries more or less folded! 



5, Orientation of body. 



In my above mentioned work (1893 a, p. 246) I urged that owing to the arrangement of 

 tile mesenterial musculature described above, which I compared with that of other Authozoa, we 

 must take the view that the directive mesenteries in Ceriantharia are dorsal directi\es, and that the 

 siphonoglyph joining these is a dorsal siphonoglyph, whilst the Zoantharia in contrast to the Ceri- 

 antharia are provided with ventral directive mesenteries and a ventral siphonoglyph. I dwelt also 

 on the fact that on this assumption not only the single multiplication zone of the mesenteries of 

 Ceriantharia but also the two similar zones of Zoantharia will be situated in the ventral (posterior) 

 portion of the body. Whilst some investigators such as Duerden (1902 p. 444) have accepted my 

 terminology, others, like van Beneden (1898) and Mc. Murrich (1910), have not adopted it. 



To begin with a criticism of van Beneden's view of the homology of the siphonoglyphs 

 and directive mesenteries, I have to insist that van Beneden in the work cited — as far as I can 

 see — forgets in one place what he has affirmed in another, witli the result that he has invohed 



■ Bovcri (1889) iu a young spccitneu described by him as a Cerianthid larval form at an S-mesentery stage, found 

 a mesenterial musculature arranged as in the genus Edwardsia — an observation which Mc. Murrich has made use of to 

 support his view of the orientation of the body. Van Beneden has already questioned the ascription to the Cerianthidae 

 of the larval form reproduced by Boveri in fig. 2, Plate 2, {1889). I can mj-self subscribe to the view of van Beneden the 

 more heartily, for the reason that a transverse section of this globular form does not at all suggest a section of a Cerian- 

 tharian larval fonn but resembles an Actiniariau form, in as much as the filaments in this case are among other things about 

 equally developed on all the mesenteries. As we know that the liemisulci answering to the filaments on the directive mesen- 

 teries are not .so sharply marked off as the filaments and all filaments are alike, it follows indisputably tliat Boveri was 

 mistaken in his identification of this larval form. On the other hand, the remaining larval forms described by Boveri with 

 the exception of the young specimen reproduced in fig. 7, Plate 21 are Cerianthidae. As the arrangement of tlie musculature 

 on the mesenteries and the presence of two couples of directive mesenteries are the characteristic marks of the Edivardsia 

 stage of development, and not the order in which the mesenteries first appear, all ground disappears for holding that Ceri- 

 antharia pass through an Edwardsia stage of development. 



